1. Field of the Invention
The present invention relates to covulcanizable polymer blends of a sulfur imide-modified terpolymer and a highly unsaturated rubbery polymer.
2. Description of Information Disclosures
Sulfur imide-modified low unsaturation terpolymers of ethylene, a higher alpha olefin and a non-conjugated diene and processes for their preparation are disclosed in U.S. Pat. Nos. 4,772,406 and 4,867,753, the teachings of which are hereby incorporated by reference.
Highly unsaturated rubbery polymers are also known and commercially available.
Mixtures of chlorothiosulfonamide-modified rubbery terpolymers having a low degree of unsaturation and a highly unsaturated rubbery polymer and vulcanizates of such mixtures are also known. See, for example, U.S. Pat. No. 3,915,907 and U.S. Pat. No. 3,970,133.
Mixtures of maleic anhydride-modified low unsaturation terpolymers and a highly unsaturated rubbery polymer are also known. See, for example, A. Y. Coran, Abstracts Rubbercon 1987, Harrogate, UK, p. 32A/1.
Blends of low unsaturation rubbery polymers with highly unsaturated rubbery polymers are desirable since they would incorporate the properties of both types of rubbery polymers. The advantages of incorporating low unsaturation rubbery terpolymers into compositions of high unsaturation rubbery polymers are known to provide improved ozone resistance to the vulcanized blend. However, low unsaturation rubbery polymers, such as, for example, elastomeric terpolymers of ethylene, propylene, and a non-conjugated diene vulcanize at a slower rate than the highly unsaturated rubbers and, therefore, attempts to covulcanize such blends may yield heterogeneous dispersions of a poorly cured or uncured low unsaturation rubber in a well cured highly unsaturated rubber and preclude the use of such blends in articles subjected to severe service requirements such as tires.
It has now been found that a blend of a sulfur imide-modified elastomeric terpolymer having a low level of unsaturation and a highly unsaturated rubbery polymer can be covulcanized (i.e., co-cured) to produce a vulcanized blend having improved properties.